Maybe Doomsday Clicker is a neat game, but it ran like butts on my gen 3 iPad. It's a bit boring to review a game poorly because of performance, but if I'm allowed to buy it on my decide and if it's 'supported', it should at least run well. Doubly so for an idle game, moving the menus around shouldn't be a time-consuming effort, with each clicks taking a few seconds to register properly. It's kinda of a shame, because at the same time, some systems in DC were interesting.
You start with a few coins, then you use that to build rooms that produce money over time, and you use that money to upgrade your rooms and buy more of them - with boosts that unlock after you buy enough upgrades for you rooms. You also can buy perks that give bonus percentages to your coin production. For watching ads, you get a coin multiplier for a period of time, and you can also tap on flying robots to get extra multipliers. The whole 'tapping on critters walking at the surface' thing is a bit weird, because while I agree that it adds something for you to do while you're waiting for your meters to fill they're just on the surface so you have to scroll up from time to time, and with my poor performance it's not a fun thing to do.
The interesting thing about Doomsday Clicker is that for each room you build - and sometimes when clicking on critters - you get humans that you can use to increase your coin production by 5% on the next run. You also can unlock other boosts when you have a large number of these humans sacrificed - increasing your money production this way requires you to reset your game, after all. I like this approach because you get to increase your multiplier quite quickly - and you can buy more spaces to build more rooms for exorbitant sums of money, so you'll need it.
In any case, I couldn't tolerate Doomsday Clicker for very long because of the performance issues. It seemed like an okay idle game, but not being able to play it in a satisfactory way lessened much the experience for me.